CONCENTRATION 335 put was for separating highly magnetic substances such as magnetite and magnetic pyrites. WetherilFs patent (U. S. 555792 March 3, 1896) was the first one to show mechanical means for producing a concentrated magnetic field, so that such feebly magnetic material as spathic iron and the ferruginous forms of blende could be attracted to the pole pieces. Magnetic separators either act on Recommended Speed 275fo 290 ft. RM. FIG. 8.óDeister slimer table. dry material or wet. Designs for treating dry material are the far more common. The principal high intensity machines are the Wetherill and the International. Magnets may be either fixed or movable. The Wetherill and the International belong to the first class. The dropping of the magnetic material is effected by causing it to pass outside of the magnetic field. This is done by: (1) preventing the magnetic material from coming in direct contact with the magnet by means of a traveling belt, or a revolving cylinder of nonmagnetic substance, to which the magnetic material will cling so long as in the magnetic field, but from which it will drop as soon as removed from it. (2) The magnetic material may be attracted directly to the pole, which by revolution or change in electrical connection may suffer a change in polarity, or become nonmagnetic, thus dropping the attracted particles after removing them from the stream of non-magnetic. (3) The magnetic material may be attracted directly to the pole, and be removed therefrom by means of a brush or scraper.